The aim of the project is to study the generation and transmission of visual signals in the vertebrate retina. Attention will be devoted to: 1) transduction of light to electrical changes in the retinal receptors, and 2) transfer and integration of visual signals at the synaptic junctions in the retinal pathways. The analysis will center on the properties of single cells or portions of single cells in eyes from cold-blooded animals with large retinal neurons. By recording the membrane current of single rod outer segments we propose to define the number of conductance channels, their permeability, kinetics, and regulation by light. To better estimate the size of the electrical effect of a single photon in turtle rods, we will examine the rod dimensions, collecting efficiency, and degree of directional selectivity. Transmission between a single photoreceptor and a ganglion cell at the retinal output can be examined without visual transduction, using a microelectrode for each cell and electrical stimuli. This approach will be used to define the minimal detectable electrical signal in the rod system, the intrinsic noise in the pathway, and the kinetics of transmission. To obtain a picture of the synaptic mechanism of directional motion selectivity in retinal ganglion cells we propose to do intracellular recording and dye injection experiments in turtle eyes. Experiments will be attempted on isolated retinal cells as a means of examining membrane properties and signal regeneration without the complications introduced by cellular interactions.